Re: yamaha 225 efi 2 stroke vs. 225 4 stroke
Even3, you better stick to your day job
.<br /><br />As an engineer, I can tell you that it makes little practical sense to have a transmission on an outboard.<br /><br />The peak power range is where maximum torque over a period of time is made. Torque at revolutions per minute (rpm) equates to horsepower.<br /><br />Transmissions are used to maintain an engine's peak power under
constant varying conditions. For example stop-and-go traffic, pulling RV's up and down I-70, through speed zones ranging from 25 mph to 65 mph, coasting at 75 mph vs. WOT at 45. Accellerating, clutching, shifting, braking, cornering, etc. Again,
constant varying conditions.<br /><br />Outboards are
specifially designed to provide maximum power under a
single given condition where the engine will be performing most of its life, like your prop turning through the water pushing a load. Usually this means
maximum boat speed at a desired engine rpm established by the outboard manufacturer. A much different and specific scenario. Outboards are not designed for constant varying conditions. The most varying conditions an outboard will see is a holeshot punch, or being underpowered in huge swells. Otherwise, its just the same old prop powering through the same old water. If your outboard use means pushing a load or racing to the bass hole, change prop pitch to attain the maximum power rpm range. Those of us who also troll with outboards know that this condition is specific and much different, so we add a smaller "kicker" to our transoms.....a motor that will operate within it's specific power range.<br /><br />Ask yourself, "do engines operating compressors, pumps, generators, etc have transmissions?" No. They operate under a given condition. Just like your prop going through water. And your outboard is specifically designed to handle this constant, steady load.<br /><br />I'm not sure what outboard powered boat you have, but none of mine have a "large surface area plowing water." They get on step. Only a small portion of the bottom runs through the water. Maybe you need a bigger engine? I will agree that friction resistance on water is greater than a rolling resistance between rubber and asphalt, but only in basic, simple terms.<br /><br />My pick-up truck (dually) has 6 tires. My RV trailer has a tripple axle. That's
another 6 tires, 12 in all. It stands 12' high and 8'6" wide. It's been known to travel up 12% grades and against 50 mph winds while running accessories like air conditioners, and charging quad banks of batteries. It has a gross weight of 19,800 lbs behind it 20,000 miles of every year. It has a 30% loss of flywheel horsepower due to drivetrain losses (transmission, differentials, transfercase, etc). At 250 hp, I get about 175 hp to the wheels. That's 50 hp
less than the Yamaha 225 4-stroke in this thread.....so say agian, which is under more load?<br /><br />FWIW, changing to a SS prop will not
always yield better performance results. There are some instances of a loss in performance or speed. Then there is the disadvantage of hitting something and losing your whole lower unit rather than just the prop. And SS props are costly. I use SS on my saltwater boats and Aluminum on the river and fresh water boats. I have an 18' fiberglass that is actually slower with a SS prop, and a 23' aluminum boat that runs out 2 mph faster with the SS. My other boats don't know the difference.<br /><br />So like I said before, if Bruce can afford the 4-stroke 225 he won't be sorry. I feel it has more to offer in many ways. If money is the issue, then he would certainly be happy with the 2-stroke 225.<br /><br />It's been fun.
